1. Field of the Invention
The present invention relates to a camera having a blurring movement correction mechanism, more precisely, it relates to a camera which is equipped with a correction mechanism that detects unintentional movement of hands holding the camera and that cancels the movement of the image formed on the film surface corresponding to the unintentional motion of hands in response to the detection results of the motion of the camera by driving an optical correction unit which is disposed on an optical path of a fixed focal length optical system or a variable focal length optical system of the camera.
2. Description of the Related Art
In general, a camera having an unintentional blurring movement correction or cancelling mechanism (which is called simply camera hereinafter) is constructed in such a way that, in an example where the camera is provided with a zoom lens as a photo-taking optical system, the photo-taking optical system is detachably arranged in the camera as an integral unit of the camera body or through a lens mount and that a film surface is disposed behind the lens system on an optical axis of the lens system.
The photo-taking optical system comprises a focusing lens group constituted from a plurality of lenses and a zooming lens group constituted from a plurality of lenses. A blurring correction optical element is disposed on an optical path of the lens groups.
The focusing lens group is driven to become an in-focus state by a focus command signal Df. The zoom lens group is driven to achieve a zooming function by a zoom command signal Dz. Also, the blurring correction lens element is driven to correct or compensate for the blur of photo-image caused by unintentional motion of hands by a blur correction command signal Da.
Next, the functional motion of each lens group is described below. The focusing lens group is driven to move forward according as the focal length is shifted to the telescopic side and according as the length to the subject to be taken is shortened.
The zoom lens group is driven to move forward according as the focal length is shifted toward the telescopic side. Similarly, the blur correction optical element is driven to move forward according as the zoom lens group is driven to move toward the telescopic side.
Next, the blur correction command signal Da is more concretely described below.
The example is the case where the oscillation motion of the camera body caused by unintentional movement of hands has an oscillation characteristic of approximately sine wave form curve (a) representing an amplitude curve that moves to the positive and negative directions from the boundary of zero level.
To correct blur of photograph, that is, to minimize or compensate for influence to the subject image on the film caused by unintentional movement of hands holding the camera body that blurs the photograph, the blur correction mechanism of the camera is arranged as follows.
First, a hand movement detection unit arranged within the camera body detects the velocity V of the hand movement within a very short period of time. Then, a movement velocity changing amount data Bk is calculated on the basis of the detected velocity data. The blur (hand movement) correction command signal Da is obtained from the velocity changing amount data Bk. The signal Da is used to drive the blur correction optical element to move in the direction in which the motion of the camera caused by the hand movement is canceled so as to prevent the image of the subject on the film surface from moving on the film surface.
The correction motion is always delayed from the actual unintentional motion of the camera.
More precisely, the movement velocity is detected at a plurality of times (t-2It), (t-It), (t), (t+It) . . . , wherein (It) represents the integration time period for each time to detect the velocity. The velocity changing amount data B.sub.k, B.sub.k-1, . . . is calculated on the basis of each velocity detection data. Then, on the basis of each velocity changing amount data B.sub.k, B.sub.k-1, . . . is calculated a camera motion velocity data V.sub.k, V.sub.k-1, . . . which is used to generate the blur correction command signal Da.
Therefore, the image formed on the film surface moves in accordance with a corrected characteristic (f) which is compensated with the use of correction characteristic (d) with respect to the movement amount characteristic (e).
However, in accordance with the above mentioned correction arrangement, only about one fourth of the total movement amount of the camera body can be corrected.
In order to improve this point of correction amount ratio, an arrangement is proposed wherein the input amount to the drive circuit for the blur correction optical element is controlled so as to converge the oscillation of the movement of the camera body at the time of driving the optical system for correcting the movement of the camera.
Such an arrangement is disclosed in Japanese Patent Application Laying Open (KOKAI) No.1-300221, for instance. In accordance with the arrangement disclosed in the patent document, the amplifying ratio of the drive circuit for the blur correcting optical element is varied in response to the output from the movement detection unit so that the oscillation movement of the camera body caused by the unintentional movement of hands is attenuated to converge.
Also, the above mentioned patent document discloses another arrangement for attenuating the movement of the camera body with the use of the above mentioned electric means for varying the amplifying ratio of the drive circuit wherein the rigidity of the oscillation detecting sensor for detecting the movement of hands holding the camera body is varied to attenuate the oscillation so as to increase the correction amount ratio of the unintentional oscillation.
On the other hand, the actual amount of the driving amount for correcting the movement of the camera varies in accordance with the length to the subject. This point is described more precisely below.
A photo-taking optical system R is constituted from a film 2 disposed at a rear portion in the camera body P and a principal point Q positioned at a front portion in the camera body. When the camera body P moves upward from the optical axis O by the length y1, an image of a subject point A1 on the optical axis O is formed at an intersection point A3 between the film 2 and a line passing through the point A1 and a point B2 which is a point at a length y1 upward from a point B1 which is an intersection point between the optical axis O and the vertical line of the principal point Q.
On the other hand, in the initial position of the camera (the position of the camera before the camera is moved), the image forming point for the subject point A1 is at a point A2 on the film which point A2 is an intersecting point of the optical axis to the film. The point A2 corresponds to a point A4 on the film after the camera is moved which point A4 is length y1 upward from the point A2. Therefore, by moving the camera body upward by the length y1, the point A4 is moved to the point A3 on the film.
Accordingly, it becomes possible to prevent the image forming point on the film from being shifted from the point A4 to A3 when the camera body is moved upward by the length y1, by shifting the photo-taking optical system on the principal point line Q from the point B1 to the point B3 which is the intersection point of the line between the points A1 and A4 to the vertical line Q.
Assuming that the length between the points B2 and B3 is represented by y2, the length from the principal point Q to the film surface is represented by x1 and that the length from the point A1 to the principal point Q is represented by x2, the following equations are satisfied. EQU y1/(x1+x2)=(y1-y2)/x2 EQU y2=(x1/(x1+x2)y2
There length y2 is influenced from the length x2 to the subject. Accordingly, it becomes desirable to correct the blur correction command signal Da with the use of the data of length from the camera to the subject.
In accordance with the camera mentioned above, blur caused by unintentional movement of hands is prevented in such a way that movement of camera due to movement of hands is detected first, that on the basis of the detection data is calculated a drive amount for driving the movement compensation optical element and that in response to the calculation result is driven the optical element.
However, in accordance with such an arrangement for correcting the blur due to the hand motion, the following problems are involved.
First, the timing point of obtaining the calculation result is inevitably retarded from the timing point of detecting the movement of the camera and also the timing point of driving the optical system for correcting the motion of the camera is inevitably retarded from the timing point of obtaining the calculation result. Accordingly, there is always some deficiency in correction amount due to the delay of each functional timing point inevitably generated in the blur correction optical system so that the movement of the camera is not satisfactorily corrected.
Such a problem may not be significant when the movement amount of hands is relatively small, since the deficiency of correction amount is also small in that case so that the practical correcting function of the optical system according to the related art mentioned above is not critically impaired. However, such a problem becomes significant when the movement amount of hands becomes large since the deficiency of correction amount becomes large as well.
Secondly, there has been no consideration to the point that the necessary movement correction amount changes according to the focal length of the photo-taking optical system, that is, the shift amount of the image position on the film surface becomes large according as the focal length becomes large even when the movement amount of the camera body itself is the same. Therefore, the unintentional movement of the camera is not satisfactorily controlled and can not be fully cancelled according to the related art mentioned above.
For example, in the case where focal length of the photo-taking optical system changes from about a wide angle of 35 mm to a telescope of 70 mm and where the blur correction system is driven on the basis of the most telescopic side in which the correction condition is most severe, when the focal length of the photo-taking optical system is arranged on the wide angle side, then the correcting function of the system becomes much more than being necessitated so that an accurate and appropriate function for correcting the unintentional motion of the camera is not achieved by the blur correction system mentioned above.
Besides, there has been no consideration to the point, either, that the necessary movement correction amount changes according to the length to the subject, that is, the shift amount of the image position on the film surface becomes large according as the length to the subject becomes small (subject comes close to the camera), even when the movement amount of the camera body itself is the same. Therefore, the unintentional movement of the camera is not satisfactorily controlled and can not be fully cancelled according to the related art mentioned above.
More precisely, in accordance with the camera of the related art mentioned above, the blur correcting optical element is driven on the basis of the movement correcting amount data which is obtained using the most frequently arranged or most common or usual length of the subject as the reference of the calculation of the correcting amount data, which impairs the accurate and reliable movement correcting operation in the wide range of subject length from a close distance to an infinite point.